There has been proposed various multiplexing techniques for increasing the efficiency of the communication channel. In recent, a MIMO (Multiple-Input Multiple-Output) technique is a method which combines multiple antennas and a signal processing technique in a transmitter and a receiver and is able to significantly increase the communication channel capacity by expanding the degree of the freedom of the communication channel even though there exist scatterers.
Also, proposed techniques that have different characteristics from the MIMO technique are an OAM (Orbital Angular Momentum) technique using the conservation of angular momentum and an angular mode-based multiplexing technique. These techniques enable to increase the communication channel capacity while even using a same frequency and a same polarization. Here, the OAM technique is a technique that has been proposed for light waves, and thus it requires various laser mode generation and a light wave synthesis technique. The angular mode-based multiplexing technique adjusts the phase of transmission or reception antenna and generates a rotation angle having the orthogonality that can be propagated on the three-dimensional space.
An antenna is an essential circuit element required for various multiplexing techniques that use the same frequency and the same polarization. The antenna must be able to adjust the phase of the electromagnetic wave radiation pattern for the expansion of the communication channel to receive or transmit signals simultaneously. Therefore, it is essential to provide a technique for efficiently controlling the phase of the array antenna elements.
FIG. 1 is an illustrative view of the structure of a unit cell of a reflectarray antenna that is primarily used in the development of a large-sized antenna. The reflectarray antenna uses a unit cell as an element of an array antenna to generate various antenna radiation patterns. For this purpose, the unit cell of a reflectarray is formed to an antenna patch 106 that is made of a metal on a dielectric substrate 104 having a ground plane 102.